This protein is a histidine-tagged (his-tagged) Moloney murine leukemia virus (M-MuLV) capsid (CA) protein. The tag is on its amino-terminus, where the M-MuLV gag matrix (MA) and p12 domains usually are located. The protein was produced in bacteria, and purified by NTA-nickel chromatography. The protein was incubated in a phosphate-saline buffer at 1 mg/ml in 10 microliters under a lipid monolayer consisting of 80% phosphatidylcholine plus 20% nickel-charged DHGN (an artificial lipid which has a head group that mimics the NTA moiety).After incubations, the monolayers plus adherent proteins were lifted onto lacey grids, wicked, and frozen in liquid ethane. EM was done on the CM12 at the U of Oregon at about -180 C, and the images were taken at 60,000x under low dose conditions. The protein appears to be arranged in a centered orthogonal plane group, with hexagonal non-crystallographic symmetry, strongly reminiscent of hexon capsomeres in projection. The data for images of untilted crystals extends to beyond 10_ resolution.